Regex: Matching by exclusion, without look-ahead - is it possible?

Question

In some regex flavors, [negative] zero-width assertions (look-ahead/look-behind) are not supported.

This makes it extremely difficult (impossible?) to state an excl

Answer 1

You can usually look for foo and invert the result of the regex match from the client code.

For a simple example, let's say you want to validate that a string contains only certain characters.

You could write that like this:

^[A-Za-z0-9.$-]*$

and accept a true result as valid, or like this:

[^A-Za-z0-9.$-]

and accept a false result as valid.

Of course, this isn't always an option: sometimes you just have to put the expression in a config file or pass it to another program, for example. But it's worth remembering. Your specific problem, for example, the expression is much simpler if you can use negation like this.